Certain bearing assemblies are known for use with the wheels of motor vehicles. Spanish Patent EP 2602123 A1, for example, describes a hub bearing unit, in this case an asymmetrical one, for the wheel of a motor vehicle, which includes a flanged hub rotatable around a rotation axis, a flange integral with the flanged hub and transverse to the axis of rotation, a stationary ring disposed radially outside of the flanged hub and provided with rolling tracks axially spaced from one another, and two rolling bodies crowns (for example, balls) arranged between the stationary ring and the flanged hub. The flanged hub integrally forms a radially inner raceway for the ball bearing axially outer, while the radially inner raceway for the balls axially inner crown is formed on an inner ring of the bearing, radially outer planted on flanged hub.
Such a bearing assembly may place considerable local loads between the bearing rings and rolling bodies, especially in the case of heavy duty applications in terms of load transmitted. Additionally, such a bearing assembly do not allow the bearing to obtain large values of resistance of the bearing and its greater duration in time. Finally, such a bearing assembly presents important axial dimensions, due to the presence of a flange integral to the flange portion and the hub transverse to the axis of rotation.
To increase the performance and especially the stiffness of the bearing, it may be preferable to increase the distance of the pressure centers. This can be achieved by increasing the diameter of the circumference of the centers of the rolling bodies (the so-called “pitch diameter” or more simply “pitch”) of the bearing. Such solutions are already known and are developed in order to significantly improve the performance. The disadvantage connected to the increase of the “pitch” is that consequently it also increases the volume, and therefore weight, dramatically with the “pitch-squared value”. This increase in weight can usually not be accepted by car manufacturers.
A further improvement is to provide an even greater increase to the diameter of the circumference of the centers of the rolling bodies, so as to be able to enter inside the bearing constant velocity joint and integrate in a single piece the so-called bell of the joint with the hub, or with the inner ring of the bearing. The integration of both components may allow the reduction of weight and cost of the entire unit. Further reduction of weight and costs may be achieved by also integrating the small inner ring of the bearing, the axially internal ring, with the bell of the joint. In other words, the hub may also assume the function of a single inner ring of the bearing and the bell of the joint at a constant speed.
The concept of single inner ring is already known in so-called third-generation bearings. The development of this feature foresaw the use of a single cage for both rolling bodies of the two tracks to be mounted on the axially inner side. This feature, the single cage, however, is not acceptable in current projects of bearing units that require more and more high performance. In fact, the single cage can create several problems. During the operation of the bearing, the contact angles of the two tracks with the corresponding rolling bodies (for example, spheres) may slightly differ relative to one another. Consequently, this may also change the points of contact between tracks and balls and, therefore, also the diameters of the circumference of the same sphere centers (“pitch”). On an equal angular speed of the wheel, the linear velocity varies proportionally to the “pitch change”. In other words, the two rows of balls may have a different speed. The cage, which performs the function of keeping the distance between the rolling bodies, however, cannot be subjected to significant forces and as typical consequence, may disintegrates or melts if overloaded.
The case of the so-called symmetrical bearing, i.e. with the same “pitch” for both crowns of rolling bodies is now analyzed. The drawbacks outlined above, are obviously also present in the case of asymmetric bearings.
Therefore, the existing high-performance solutions, which adopt a single inner ring, require a new mounting procedure, compared to the standard applications now used.